There has been attempted a technique for decontaminating earth or underground water polluted by chlorinated ethylene or chlorinated ethane, wherein the chlorinated ethylene or chlorinated ethane is subjected to an anaerobic microbiological dechlorination (decomposition) using dechlorination bacteria existing originally in the polluted earth or underground water. For treating the polluted earth or underground water, it has been proposed to introduce such dechlorination bacteria into the polluted earth or underground water. It has been confirmed that such dechlorination bacteria can decompose not only chlorinated ethylene but also chlorinated ethane by means of a chlorinated ethylene-decomposing enzyme present in such dechlorination bacteria. Such a known technique may encounter a problem that it is not guaranteed that a better treating performance, namely, a complete dechlorination will always be attained.
For this reason, there has been a demand for an established method for discriminating preliminarily whether a contemplated dechlorination performance will be attained or not, in the case of treating earth or underground water polluted by chlorinated ethylene and/or chlorinated ethane using dechlorination bacteria. There is further a demand for a method for treating polluted earth or polluted underground water, in which the decontamination can be realized efficiently within a brief time in a reliable manner by utilizing a high performance dechlorination bacterium having a high dechlorination activity selected among the existing dechlorination bacteria.